1. Field of the Invention
The present invention relates to a system for processing signals or data. More specifically, the invention relates to a system for decomposing and recomposing wavelets with minimum filter delay.
2. Background
As the transmission size or transmission rate of video data increases, the need for effective and efficient compression and decompression becomes more important. Although compression and decompression techniques are important, these techniques must be performed in a manner that preserves the quality of the image or video data being transmitted. Thus, competing goals exist in 1) maximizing the compression of video data to minimize transmission time along a transmission medium and 2) providing a high quality image after transmission and decompression of the video data. Minimizing transmission time is particularly important in systems transmitting real-time video data.
Using known techniques, it is possible to maximize compression, thereby minimizing transmission time or transmission bandwidth, by sacrificing image quality. Conversely, known techniques are available for providing a high quality decompressed image by performing a minimal amount of compression, thereby increasing the required transmission time or transmission bandwidth.
Other known image processing systems use a conventional block transform technique such as Discrete Cosine Transform (DCT). DCT transforms an image one dimension at a time. DCT first evaluates an image and converts the image into horizontal pixel values. Next, DCT evaluates the image and converts the image into vertical pixel values. This type of block transform technique generates large digitized data files associated with the image. Additionally, since the image is evaluated twice, the image is accessed from memory twice, thereby increasing the overall processing time.
Other image processing systems use techniques involving wavelet technology. A wavelet transforms an image into multiple frequency bands. Each frequency band contains the image at a quarter resolution of the original image, in varying degrees of image quality. As the bands progress from a low frequency to a high frequency, the image quality increases. The lowest frequency band is generally the most important band for visual sensitivity. Therefore, the lowest frequency band is typically the first band transmitted, and the highest frequency band is typically the last band transmitted. Thus, if only the low frequency band is received, the major features of the image are visible even though the information contained in the remaining higher frequency bands is not displayed.
When wavelet techniques are used in a CODEC (Coder-Decoder) system, the CODEC consists of a wavelet decomposition module that breaks the image into bands with lower resolution and a wavelet recomposition module that transforms bands into the image with original resolution.
A wavelet composition module calculates a compressed value of a particular pixel by determining the pixel values of pixels surrounding the particular pixel. Using various averaging techniques, the compressed value for the particular pixel is calculated. This type of pixel calculation is slow due to the time-consuming and calculation-intensive process involved in determining surrounding pixel values for each pixel in the image.
A filtering operation is performed during a wavelet decomposition procedure and a wavelet recomposition procedure. Known techniques for implementing the filtering operation generally cause filter delay (i.e., a time delay as the wavelet is decomposed or recomposed).
It is therefore desirable to provide a technique for efficiently composing and decomposing wavelets without the delay associated with known systems.